1. Field of the Invention
The present invention relates generally to suspension systems for hard disk drive systems. More specifically, the present invention relates to piezoelectric micro-actuators for hingeless actuation of loads in hard disk drive head suspension assemblies.
2. Related Art
Microactuators have many applications. For example, in the magnetic disk drive industry, piezoelectric (hereinafter “piezo”) microactuators have become an attractive alternative to voice coil actuators, particularly in high-density applications. As industry trends have demanded higher density storage capabilities, piezo actuators have been more frequently employed in HDD systems because they allow for more precise radial positioning of the head with respect to the disk.
A conventional suspension assembly in an HDD comprises a base plate, load beam, flexure, one or more actuators, a slider, and circuit elements for energizing the actuator. In order to achieve the desired angular motion at the head, or load end, of the assembly, most HDD piezo microactuator designs rely on hinges to convert the linear motion of a piezo actuator into angular motion. One conventional method of achieving higher precision is to design a head positioner having dual piezo actuators, which work in a push-pull mode about one or more hinges that define the center of rotation. Numerous examples exist in the prior art, such as in U.S. Pat. No. 6,046,888; U.S. Pat. No. 6,157,522; and U.S. Pat. No. 6,331,923. In other designs, a single piezo element is used, such as in U.S. Pat. No. 6,522,050 and U.S. Pat. No. 6,760,196. In single-piezo actuator designs, reliance on hinges to effect rotation is even more pronounced. In general, in all of the suspension assemblies described in the foregoing patents, the coupling of a hinge to the piezo actuator adds to the manufacturing complexity.
Effecting multiple piezo lead connections can be troubling, and in any case burden the manufacturing process with additional steps. This is especially true in dual-piezo configurations having flexible circuits that require stitch bonding or lengthy tail weaving. These techniques entail excessive delicate manual operations to weave, fixture, and tack solder the connections. In typical prior art designs, the piezo is mounted to the upper surface of the load beam (the surface opposite the air bearing), while the flex on circuit (FOS) runs beneath the load beam. This arrangement requires an FOS having an extended tail portion woven to a soldering location on the upper surface of the piezo, and causes manufacturing difficulties: extended tail weaving in this fashion undesirably reduces assembly packing density; installing solder bumps on the flexure add significant fabrication cost; and the thermal soldering operation itself can degrade piezo performance as it often exceeds the Curie temperature of the actuator.
Dual actuator designs cause performance tradeoffs as well. HDD suspensions are designed to possess high bending, torsion, and sway frequencies to achieve good dynamic performance characteristics. However, inclusion of a hinge or a second actuator into the suspension tends to degrade its frequency response. This is typically a result of weak coupling properties of the piezo-hinge structure at both the front and distal ends of the suspension. Addition of piezo mass also contributes to the degradation. In some prior art, stiffeners are provided to strengthen the coupling of the distal end, but this adversely affects actuator performance by reducing the attainable stroke levels. Stiffeners also introduce windage-induced turbulence on the head, due to their geometric features being out of plane. Other solutions include increasing the flexibility of the hinge, and moving the hinge closer to the actuator body. But these techniques concentrate more stress on the hinges, leading to early fatigue and material failure.
In view of the foregoing, there is an ongoing need to improve the performance and manufacturability of microactuators in disk drive suspension systems.